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Solids

Any compound which occupies volume in nature is called as states of matter and is classified as Solids, Liquids and Gases. These states depend on their volume, temperature and pressure.

Definition: A compound having an ordered repeating pattern and have definite mass and shape is called solid.

Properties:
·  Definite mass
·  Definite volume and shape
·  Short intermolecular distance
·  Strong intermolecular forces
·  Rigid and incompressible



Classification of solids:
Solids are divided into two types, amorphous solids and crystalline solids.


Crystalline compounds are further classified on the basis of nature of crystals and bonding among them.
1. Ionic solids:
Solids in which particles are bonded between anions and cations are called as ionic solids.

Properties:
·  Hard and brittle in nature
·  High melting and boiling points
·  Electric insulators as ions are not free to move
·  Conduct electricity when dissolve in water

Example: NaCl, KBr


2. Molecular solids:
Solids in which molecules are the constituent particles are called as molecular solids. They are again divided into three types.
 

Non-Polar molecular solids:
Molecules are held by weak dispersion forces or by non-polar covalent bond.
 
Properties:
·  Soft in nature
·  Non-conductors of electricity
·  Low melting point

Example: Iodine, Argon, Helium, CCl4


Polar molecular solids:
Solids in which molecules are held by strong dipole-dipole interactions are called polar molecular solids.

Properties:
·  Soft and non-conductor of electricity
·  Melting point is higher then non-polar molecular solids
 
Example: Solid SO2, Solid NH3, HCl


Hydrogen bonded molecular solids:
Solids in which molecules are held by strong hydrogen bond are called as hydrogen bonded molecular solids

Properties:
·  Non conductor of electricity

Example: Solid SO2, Solid NH3, HCl


3. Metallic solids:
Solids in which molecules are held by metallic bonds i.e. electrons are free and evenly spread out throughout the crystal.

Properties:
·  High electrical conductivity
·  High thermal conductivity
·  Wide range of Melting points

Example: Sodium, Zinc, Copper, Ferrous


4. Covalent solids:
Solids in which molecules are held by covalent bond are called covalent solids

Properties:
·  Hard and brittle
·  High melting point
·  Non-electricity conductor

Example: Diamond, silicon carbide.


Crystal lattice:
Crystalline solids are made up of a regular pattern of constituent particles. The arrangement of these particles is often depicted in the form of a tree dimensional array of points which is called as crystal lattice.

Crystal lattice is defined as a pattern of points which describes a regular three dimensional arrangement of particles in a crystal.

Each lattice point gives the location of one particle in space.

There are 14 different types of lattices are possible, which are called Bravis lattices.


Unit cell:
Each lattice is generated by repeating small characteristics portion, called as Unit cell. Unit cell is a smallest portion of crystal lattice and is characterized by its edge lengths and the angles between these edges. Unit cell is divided into two categories.

Primitive unit cell:
Particles are present at the corner position of a unit cell

Centered unit cell:
An additional particles is present other than corner position of a unit cell
·  Face centered unit cell: An additional particle is present at centre of each face.
·  Body centered unit cell: An additional particle is present at their body centre.
·  End centered unit cell: An additional particle is present at centre of two opposite faces.

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